atyfb: set FBINFO_READS_FAST

Set FBINFO_READS_FAST so that the console code uses scrolling instead of
rewriting. This improves scrolling speed.

A time to do ls -la /usr/bin:
	original patched
32bpp	4.9	3.6
24bpp	4.9	2.9
16bpp	4.9	2.1
8bpp	4.9	1.7

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>